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<br />I <br />I <br />I <br />I <br />I <br />I, <br />I <br />I <br />I <br />I <br />I <br />i <br />I <br />I <br />II <br />I <br />I <br />I <br />I <br /> <br />EXECUTIVE SUMMARY <br /> <br />Researchers examined the fish communities of the Colorado and San Juan river interface zones <br />of Lake Powell during 1999 and 2000. The objectives were to: (1) search for young razorback <br />sucker and Colorado pikeminnow and, if found, PIT tag them; (2) examine the effectiveness of <br />various collection techniques on juvenile native fish; and (3) describe the fish communities found <br />in these transitory, or actually "migratory" habitats. The San Juan River interface zone was <br />sampled 5 times each year during the spring and summer while the Colorado River site was <br />sampled a total of 3 times over the 2-year period, all in the spring. <br /> <br />Lake Powell's surface elevation fluctuated 5.3 m during the course ofthe study. Elevational <br />changes caused the reservoir/river interface zone to advance up and retreat down the San Juan <br />River> 15 km. Over 1,000 ha of bottomland at Piute Farms was flooded and drained in 1999 <br />alone. Sampling focused on these migratory habitats. <br /> <br />Nearly 40,000 fish were captured using seines, light traps, electrofishing, minnow traps, fyke <br />nets, and trammel nets. Twenty three species were represented, only 5 species were endemic to <br />the watershed. The fish community was far more indicative of the Mississippi River basin than <br />Colorado River ichthyofauna. Numerically, nonnative fishes dominated the sample (99.4%) <br />while natives only represented 0.6% of the fish collected. Thirteen adult razorback suckers were <br />captured, all believed to be hatchery stocked. No juvenile razorback suckers were found. Three <br />juvenile Colorado pikeminnow and one small chub (Gila spp.) were collected. Flannelmouth <br />sucker was the most common large native species, however, they represented only 0.4% (41) of <br />the fish captured. Two species not previously reported were the white crappie (Promoxis <br />annularis) and gizzard shad (Dorosoma cepedianum). <br /> <br />The most common fish were red shiner, threadfin shad, common carp, striped bass, and channel <br />catfish. Relative abundance was higher at the inflow area compared to a reservoir control site <br />(Spencer' s Camp). Common carp and bullhead sp. were twice as abundant in inflow habitats <br />compared to the reservoir whereas smallmouth bass and green sunfish were less abundant. <br />Species composition and abundance were influenced by habitat availability. For example, adult <br />striped bass and walleye were more common in channel habitat while broad flood plain habitat <br />supported more black crappie and juvenile fish. <br /> <br />Native fish were taken by a variety of sampling methods. No single technique proved effective <br />for a particular species; sampling success was more indicative of life stage. Three species of <br />larval suckers (razorback (2), flannelmouth (3), and possibly bluehead (2)) were captured in light <br />traps. A juvenile Gila spp. and three juvenile Colorado pikeminnow were captured by minnow <br />trap, seine, and trammel net, respectively. The majority of adult flannelmouth (36 or 86%) and <br />razorback suckers (11 or 92%) were taken by trammel net. However, two (8%) razorback sucker <br />were captured by electrofishing and 5 (14%) flannelmouth suckers were taken by hoop net. <br /> <br />v <br />